Two-dimensional vertical fins

ABSTRACT

A method of forming a two dimensional (2D) vertical fin is provided. The method includes heat treating a periodic array of irregular openings in a substrate, wherein there are walls of substrate material between adjacent openings, to reduce the surface area of the openings, and etching the openings with a crystal-plane selective etch to form squared openings in the substrate.

BACKGROUND

The present invention generally relates to vertical fins extending intwo lateral dimensions, and more particularly to fin field effecttransistor (FinFET) devices having fins extending in two lateraldimensions.

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the device channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and FinFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the FinFET can be an upright slab of thin rectangularsilicon (Si), commonly referred to as the fin with a gate on the fin, ascompared to a metal-oxide-semiconductor field effect transistor (MOSFET)with a single gate parallel with the plane of the substrate. Dependingon the doping of the source and drain, an NFET or a PFET can be formed.Two FETs also can be coupled to form a complementary metal oxidesemiconductor (CMOS) device, where a p-type MOSFET and n-type MOSFET arecoupled together.

SUMMARY

In accordance with an embodiment of the present invention, a method offorming a vertical fin having multiple arms is provided. The methodincludes heat treating a periodic array of irregular openings in asubstrate, wherein there are walls of substrate material betweenadjacent openings, to reduce the surface area of the openings, andetching the openings with a crystal-plane selective etch to form squaredopenings in the substrate.

In accordance with another embodiment of the present invention, a methodof forming a vertical fin having multiple arms is provided. The methodincludes forming a periodic array of irregular openings in a substrate,wherein there are walls of substrate material between adjacent openings.The method further includes heat treating the substrate and openings toreduce the surface area of the openings, and etching the openings with acrystal-plane selective etch to form squared openings in the substrate.

In accordance with yet another embodiment of the present invention, atwo-dimensional vertical fin field effect transistor device is provided.The device includes a two-dimensional vertical fin having intersectingarms with atomically sharp corners where perpendicular crystal planesmeet.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a top view showing a periodic array of irregular openingsformed in a substrate, in accordance with an embodiment of the presentinvention;

FIG. 2 is a top view showing the irregular openings partially reflowedto increase the shape regularity, in accordance with an embodiment ofthe present invention;

FIG. 3 is a top view showing the elliptical openings further reflowed toincrease the shape regularity and form rounded openings, in accordancewith an embodiment of the present invention;

FIG. 4 is a top view showing the rounded openings etched by a crystalplane selective etch to form squared openings in the substrate, inaccordance with an embodiment of the present invention;

FIG. 5 is a top view showing the squared openings selectively masked, inaccordance with an embodiment of the present invention;

FIG. 6 is a top view showing two-dimensional vertical fins formed fromthe masked, squared openings, in accordance with an embodiment of thepresent invention;

FIG. 7 is a top view showing the squared openings covered by a largermask to form an extended vertical fin array, in accordance with anembodiment of the present invention;

FIG. 8 is a top view showing two-dimensional lattice-type vertical finformed from the masked, squared openings, in accordance with anembodiment of the present invention;

FIG. 9 is a top view showing the squared openings covered by an extendedmask, in accordance with an embodiment of the present invention;

FIG. 10 is a top view showing two-dimensional fence-type vertical finsformed from the masked, squared openings, in accordance with anembodiment of the present invention;

FIG. 11 is a top view showing a periodic hexagonal array with horizontalrows of irregular openings formed in a substrate, in accordance with anembodiment of the present invention; and

FIG. 12 is a cut-away orthographic view of a fin field effect transistor(FinFET) device formed from a cross-type vertical fin, in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention relate to two-dimensional verticalfins and fin field effect transistor (FinFET) devices having multiplearms extending from points of intersection to form a two-dimensional(2D) vertical fin when viewed from the top. The vertical fins can extendvertically from a substrate surface and have multiple arms extending intwo lateral dimensions parallel to the plane of the substrate, where thearms of the vertical fin can intersect at perpendicular angles. Multiplevertical fins can cross each other to form a two-dimensional crossshape, fence, or lattice structure, when viewed from the top. Toincrease the effective transistor width and thus increase the drivecurrent for a given footprint of a chip area, a two-dimensional (2D) fincan be used instead of one-dimensional (1D) fin (e.g., a vertical finwithout arms or branch points, a linear vertical fin). A two-dimensionalvertical fin can have a cross shape, an H-shape, a fence shape, or alattice-shape, where two or more arms intersect at square corners.

Embodiments of the present invention relate to the fabrication oftwo-dimensional vertical fins and fin field effect transistor (FinFET)devices having a two-dimensional vertical fin. Two-dimensional verticalfins can be formed from a regular (or periodic) array of openings in asubstrate using a subtractive etch that leaves the intervening wallsbetween adjacent openings (e.g., vias) as fins extending upwards fromthe etched substrate surface.

Embodiments of the present invention relate to two-dimensional verticalfins and fin field effect transistor (FinFET) devices having reducedcorner rounding at the intersection of the perpendicular arms formingthe vertical fin. Rounded corners at the intersection of the 2D fin arms(i.e., corner rounding) can cause variations in fin channel thicknessand thus device performance variations between different devices on thesame region of the substrate.

Embodiments of this invention provide a fabrication method that forms a2D fin with sharp corners at the intersection of the fin arms by using a2-step process—(1) annealing to reduce the irregularity of the shape oftrench sidewalls, and (2) performing a crystalline orientation dependentetching to sharpen the corners of 2D fin. Use of an etch chemistry thatis selective for a particular crystal plane (e.g., {110}) of thesemiconductor substrate material can form consistent, sharp corners atthe intersection of the perpendicular arms forming the vertical fin(s),which reduces the variation in device geometries, fin channelthicknesses, and device performance characteristics. The corners at theintersection of the perpendicular arms can be square corners, where theperpendicular crystal plane (e.g., {110} and {−110}) meet atapproximately 90 degrees (+/−1 degree). In various embodiments, atwo-dimensional vertical fin can have intersecting arms with atomicallysharp corners, where perpendicular crystal planes meet.

Embodiments of the present invention relate to the fabrication ofvertical transport fin field effect transistor (VT FinFET) deviceshaving a two-dimensional vertical fin with two-dimension topsource/drains and wrap-around gate structures. A top source/drain can beepitaxially grown on the top surface of the two-dimensional vertical finto have the matching shape. A gate dielectric layer can be conformallyformed on the various parallel and intersecting walls of thetwo-dimensional vertical fin, and a gate conductor can be formed aroundthe device using a blanket deposition and patterning techniques.

Exemplary applications/uses to which the present invention can beapplied include, but are not limited to: logic device (e.g., gates,processors, FPGAs, etc.), memory devices (e.g., SRAM, DRAM), andapplication specific integrated circuits (ASICs).

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a top view of a periodicarray of irregular openings formed in a substrate is shown, inaccordance with an embodiment of the present invention.

In one or more embodiments, a series of openings 120 (i.e., holes, vias,cavities, etc.) can be formed in a substrate 110, where the openings 120can be formed in a regular or periodic array. The array can be in asquare lattice (i.e., rows and columns), a rectangular lattice, or ahexagonal lattice with vertical columns or horizontal rows, althoughother period array are also contemplated. The openings 120 can be formedby lithography and etching (or any other suitable patterning techniques,such as self-aligned multiple patterning (SAMP)), where the openings 120can have an irregular shape. In various embodiments, the openings canhave an irregular shape that is lobular or rectangular with or withoutprotuberances, where the lobes or protuberances can be at the corners ofsquare or rectangular shaped openings 120. The interior surfaces of theopenings 120 can also be rough and uneven. The etching can be aselective, directional etch, for example, a reactive ion etch (RIE).

In various embodiments, the substrate 110 can be a semiconductormaterial. In various embodiments, the substrate 110 can be singlecrystal silicon (c-Si) substrate. The single crystal silicon can have{110} crystal planes perpendicular to the surface of the substrate. Invarious embodiments, silicon-germanium (SiGe) and germanium (Ge)materials can be used as the substrate, where they have similarcrystalline structure compared to silicon (Si) that providesperpendicular crystal planes (e.g., {110}) that can be selectivelyetched. In various embodiments, the substrate material can be a III-Vsemiconductor material, where the substrate has, for example, a {111}crystal plane that be selectively etched.

In various embodiments, the openings can have a diameter in a range ofabout 15 nanometers (nm) to about 100 nm, or about 30 nm to about 50 nm,although other diameters are also contemplated. The diameter can becalculated as the average of the length of the line which connects thetwo farthest boundary points and passes through the centroid (C) and thelength of the line which connects the two nearest boundary points andpasses through the centroid.

In various embodiments, the openings 120 can be separated by a wall 112having a thickness in a range of about 5 nm to about 20 nm, or about 10nm to about 15 nm, although other thicknesses are also contemplated. Thewall thickness can be the average of the distances between multiplepoints horizontally, vertically, or diagonally opposite reference pointson an opening 120 (and parallel with the period planes of the lattice).The openings 120 can be arranged in a regular pattern having apredetermined pitch that determines the thickness of the walls 112between the openings. A rectangular lattice can provide walls withdifferent thicknesses laterally between openings in the same row orcolumn. A rectangular lattice can have walls with different thicknessesbetween horizontally adjacent openings compared to vertically adjacentopenings.

FIG. 2 is a top view showing the irregular openings partially reflowedto increase the shape regularity, in accordance with an embodiment ofthe present invention.

In one or more embodiments, the substrate 110 with the openings 120 canbe heat treated 99 to allow the material of the substrate to reflowunder the force of surface free energy to increase the regularity of theopenings' shapes and convert the irregularly shaped openings 120 firstto elliptically shaped openings 122 then to round openings. Withoutintending to be limited by theory, it is believed that high energyfeatures, such as corners, lobes, and protuberances, as well as surfaceroughness, can become more rounded or eliminated to reduce the perimeterand surface area of each of the openings and thereby reduce the surfacefree energy of the openings 120. The surface free energy (also referredto as surface energy) quantifies the disruption of intermolecular bondsthat occur at a surface, and therefore atoms at a surface or interfacecan have a higher energy than atoms within the bulk of a material thatare fully coordinated. A larger surface implies a higher surface energy.A reduction in surface area can reduce the surface free energy andincrease the stability of a surface. By increasing the temperature, moreatoms can achieve the activation energy to migrate to coordinationpositions that reduce the number of surface atoms. At highertemperatures a solid material can creep, such that the volume of thesolid remains essentially the same but the surface area changes. Thesurface energy can be anisotropic, such that different crystal face of acrystalline material have different free energies, that can affect thechange in surface areas of different crystal faces. For example, the(111) plane of single crystal silicon has a measured surface energyreported as 1240 mJ/m². In various embodiments, the irregularly shapedopenings 120 can reflow into elliptically-shaped openings 122, as thelobes or protuberances are eliminated and the radii of corner(s)increase. The surface roughness of the openings can also be reduced bythe heat treating and reflow. The elliptically-shaped openings 122 canremain in the square, rectangular, or hexagonal lattice arrangement asthe openings undergo the heat treatment.

In various embodiments, the heat treatment can be a furnace anneal, arapid thermal anneal (RTA), a flash anneal, a laser anneal, or anysuitable combination of the annealing techniques.

In various embodiments, the heat treatment can be conducted at atemperature in a range of about 400° C. to about 1200° C., or about 600°C. to about 1000° C., or about 700° C. to about 900° C., although othertemperatures below the melting point of the substrate material are alsocontemplated.

In various embodiments, the heat treatment can be conducted for aduration in a range of about 5 seconds (sec) to about 30 minutes (min),or about 30 sec to about 10 min, or about 30 sec to about 3 min. Theannealing time can depend on the heat treating temperature and substratematerial, where, for a given substrate material, the higher theannealing temperature, the shorter the annealing time can be.

In various embodiments, the heat treatment can be conducted in areducing atmosphere, for example, hydrogen gas (H₂), deuterium (D₂), andcombinations thereof. In various embodiments, the annealing environmentmay further include other chemically inert gases, including, but notlimited to, nitrogen (N₂), helium (He), argon (Ar), neon (Ne), andcombinations thereof.

In various embodiments, the heat treating atmosphere can be at apressure in a range of about 10 milli-Torr (mTorr) to about 10 Torr, orabout 30 mTorr to about 200 mTorr, although other pressures are alsocontemplated, where the pressure includes the reducing and inert gassespresent. The listed ranges of annealing temperature, time, and pressure,are not intended to be limiting.

FIG. 3 is a top view showing the elliptical openings further reflowed toincrease the shape regularity and form rounded openings, in accordancewith an embodiment of the present invention.

In one or more embodiments, the heat treatment can be continued untilthe elliptically-shaped openings 122 become circular openings 124 byminimizing the surface free energy. The elliptical openings 122 can beconverted to round circular openings 124.

FIG. 4 is a top view showing the rounded openings etched by a crystalplane selective etch to form squared openings in the substrate, inaccordance with an embodiment of the present invention.

In one or more embodiments, the openings can be etched using a crystalplane selective etch to form square openings 126 from the circularopenings 124, where the crystal plane selective etch can depend on thematerial selected for the substrate 110. If the etch is performed afterforming the structure shown in FIG. 2, with elliptically-shapedopenings, then after etching the opening shape will be rectangular. Invarious embodiments, the crystal plane selective etch can be conductedfor a period of time sufficient to square the corners at intersectingarms of the two-dimensional vertical fin, where a squared opening orintersection has a radius of less than half the initial radius formed atintersecting arms by lithographic processes without a subsequent crystalplane selective etch.

In various embodiments, the etch can be a wet etch or gas phase etch. Acrystal plane selective etch can be chosen based on the substratematerial being etched. For a wet chemical etch, an aqueous solutioncontaining any of following etchants may be used: ammonium hydroxide (inaqueous solution) (NH₄OH), tetramethyl ammonium hydroxide (TMAH,(CH₃)₄NOH), ethylene diamine and pyrocatechol (EDP), potassium hydroxide(KOH), and suitable combinations thereof. In various embodiments, thewet etch temperature can be in a range of about 0° C. to about 90° C.,or about 23° C. to about 75° C., although other temperatures are alsocontemplated.

In various embodiments, the etch can be a gas phase etch, including, butnot limited to hydrogen chloride (HCl), where the etch can be conductedat a temperature in a range of about 450° C. to about 800° C., althoughother temperatures are also contemplated.

In a non-limiting exemplary embodiment, an ammonia wet etch (ammoniumhydroxide (NH₃OH)) can be used to selectively etch the {110} planes (and{−110} planes) of single crystal silicon (Si) to form square openings126 in the substrate 110. The ammonia wet etch is self-limiting, so theammonia etch can be used to form atomically sharp corners in each of thecircular openings 124 where the {110} and {−110} planes intersect byletting the etch go to completion.

FIG. 5 is a top view showing the squared openings selectively masked, inaccordance with an embodiment of the present invention.

In one or more embodiments, portions of the square openings 126 andintervening walls 112 can be covered by a mask 130, which can include ahard mask, a soft mask, or both. The mask 130 can be patterned usinglithographic techniques and etching to expose portions of the squareopenings 126 and surrounding substrate 110, but cover portions of two ormore intersecting walls 112. In various embodiments, two perpendicularwalls 112 and four square openings 126 in a square arrangement can be atleast partially covered by the mask 130 to form a cross-shaped 2Dvertical fin or H-shaped 2D vertical fin.

FIG. 6 is a top view showing two-dimensional vertical fins formed fromthe masked, squared openings, in accordance with an embodiment of thepresent invention.

In one or more embodiments, a cross-shaped vertical fin 115 can beformed be removing the surrounding portions of the substrate, while themasked portion of the walls 112 between four (4) square openings 126remain on the substrate 110. An H-shaped vertical fin 116 can be formedbe removing the surrounding portions of the substrate, while the maskedportion of the walls 112 between six (6) square openings 126 remain onthe substrate 110.

In various embodiments, the mask(s) 130 can be removed after etching thesubstrate 110 to form the cross-shaped vertical fin 115 or H-shapedvertical fin 116. The mask can be removed by ashing, selective etching,or a combination thereof.

FIG. 7 is a top view showing the squared openings covered by a largermask to form an extended vertical fin array, in accordance with anembodiment of the present invention.

In one or more embodiments, portions of the square openings 126 andintervening walls 112 can be covered by a mask 130, where a larger mask130 can cover square openings 126 and the intervening walls 112 inmultiple rows and columns. A predetermined number of M rows and Ncolumns of square openings 126 can be covered by the mask 130 to form alattice-type vertical fin having multiple intersecting walls 112, whereM>3 and N>3.

FIG. 8 is a top view showing two-dimensional lattice-type vertical finformed from the masked, squared openings, in accordance with anembodiment of the present invention.

In various embodiments, the mask(s) 130 can be removed after etching thesubstrate 110 to form the lattice-shaped vertical fin 117. In variousembodiments, arms can extend away from the intersections varyingdistances based on the lithography tolerances and mask 130 dimensions.Entire square openings 126 that were covered by a mask 130 can remainwithin four intersecting walls.

FIG. 9 is a top view showing the squared openings covered by an extendedmask, in accordance with an embodiment of the present invention.

In one or more embodiments, multiple masks 130 can be formed on thearray of square openings 126 to form a plurality of two-dimensionsFinFET devices on a region of the substrate 110, where the plurality ofmasks 130 can be laid out in a regular pattern on the substrate. Thenumber of intersecting walls forming each of the FinFET devices can bedetermined by the intended drive current for the devices. MultipleFinFET devices with improved uniformity can be fabricated on thesubstrate due to the selective etching and sharp corners formed at theintersections for each of the vertical fins.

FIG. 10 is a top view showing two-dimensional fence-type vertical finsformed from the masked, squared openings, in accordance with anembodiment of the present invention.

In various embodiments, the mask(s) 130 can be removed after etching thesubstrate 110 to form the fence-type vertical fins 118. The heights ofthe vertical fins can be determined by the depth of the directional etchused to remove the surrounding substrate 110. In various embodiments,several different vertical fin shapes can be formed on the samesubstrate 110 by controlling the mask size and layout over the openings.

FIG. 11 is a top view showing a periodic hexagonal array with horizontalrows of irregular openings formed in a substrate, in accordance with anembodiment of the present invention.

In various embodiments, the openings 120 can be arranged in a periodichexagonal array with horizontal rows, where the openings are staggeredbetween rows. The hexagonal arrangement can be used to form 2D verticalfins with I shapes and square shapes, which are different from theshapes of the vertical fins formed by a rectangular or square lattice ofopenings.

FIG. 12 is a cut-away orthographic view of a fin field effect transistor(FinFET) device formed from a cross-type vertical fin, in accordancewith an embodiment of the present invention.

In one or more embodiments, a bottom source/drain 140 can be formedbelow the vertical fin(s), where the bottom source/drain 140 can beformed from a substrate including a doped (e.g., n-type or p-type) layerand fin layer on the doped layer. The fin layer and doped layer can beepitaxially grown on a surface of a carrier layer of the substrate. Invarious embodiments, the doped layer can be etched to form an extensionregion 145 below the vertical fin, for example, a cross-shaped verticalfin 115.

In one or more embodiments, a bottom spacer layer 150 can be formed onthe bottom source/drain 140 and extension region 145 if present. Thebottom spacer layer 150 can be a dielectric material, for example,silicon oxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), alow-k dielectric material, or a combination thereof. A low-k dielectricmaterial can be, for example, fluorine doped silicon oxide (SiO:F),carbon doped silicon oxide (SiO:C), hydrogen silsesquioxane (HSQ) andmethylsilsesquioxane (MSQ), tetraethoxysilane (TEOS), and combinationsthereof.

In one or more embodiments, a gate dielectric layer 160 can be formed onthe vertical fin (e.g., cross-shaped vertical fin 115) using a thermaland/or chemical oxidation, for example, thermal oxidation, chemicaloxidation, thermal nitridation, plasma oxidation, plasma nitridation, aconformal deposition, for example, atomic layer deposition (ALD) plasmaenhanced ALD (PEALD), or a combination thereof. The gate dielectriclayer 160 can be a high-k dielectric material.

In one or more embodiments, the gate dielectric layer 160 can be anelectrically insulating dielectric material, including but not limitedto, silicon oxide (SiO), silicon nitride (SiN), silicon oxynitride(SiON), high-k materials, or any combination of these materials.Examples of high-k materials include, but are not limited to, metaloxides, such as hafnium oxide (HfO), hafnium silicon oxide (HfSiO),hafnium silicon oxynitride (HfSiON), lanthanum oxide (LaO), lanthanumaluminum oxide (LaAlO), zirconium oxide (ZrO), zirconium silicon oxide(ZrSiO), zirconium silicon oxynitride (ZrSiON), tantalum oxide (TaO),titanium oxide (TiO), barium strontium titanium oxide (BaSrTiO), bariumtitanium oxide (BaTiO), strontium titanium oxide (SrTiO), yttrium oxide(YO), aluminum oxide (AlO), lead scandium tantalum oxide (PbScTaO), andlead zinc niobite (PbZnNbO). The high-k material may further includedopants, such as lanthanum (La), aluminum (Al), magnesium (Mg), andcombinations thereof.

In various embodiments, the gate dielectric layer 160 can have athickness in a range of about 1 nm to about 5 nm, although otherthickness are also contemplated.

In one or more embodiments, a conductive gate fill 170 can be formed onthe bottom spacer layer 150 and gate dielectric layer 160 to form a gatestructure on the vertical fin. The gate structure can wrap around thevertical fin. In various embodiments, a work function metal (WFM) layercan be formed between the gate dielectric layer 160 and the conductivegate fill 170. Also, the conductive gate fill 170 can be a WFM, orinclude a WMF with other conductive material(s).

In one or more embodiments, the conductive gate fill 170 can be aconducting material, including but not limited to, doped polycrystallineor amorphous silicon (p-Si, a-Si), germanium (p-Ge, a-Ge), silicongermanium (p-SiGe, a-SiGe), a metal (e.g., tungsten (W), titanium (Ti),tantalum (Ta), ruthenium (Ru), hafnium (Hf), zirconium (Zr), cobalt(Co), nickel (Ni), copper (Cu), aluminum (Al), platinum (Pt), tin (Sn),silver (Ag), gold (Au), a conducting metallic compound material (e.g.,tantalum nitride (TaN), titanium nitride (TiN), tantalum carbide (TaC),titanium carbide (TiC), titanium aluminum carbide (TiAlC), tungstensilicide (WSi), tungsten nitride (WN), ruthenium oxide (RuO₂), cobaltsilicide (CoSi), nickel silicide (NiSi)), transition metal aluminides(e.g. Ti₃Al, ZrAl), TaC, TaMgC, carbon nanotubes, conductive carbon,graphene, or any suitable combination of these materials.

In one or more embodiments, the work function metal (WFM) layer can be anitride, including but not limited to titanium nitride (TiN), titaniumaluminum nitride (TiAlN), hafnium nitride (HfN), hafnium silicon nitride(HfSiN), tantalum nitride (TaN), tantalum silicon nitride (TaSiN),tungsten nitride (WN), molybdenum nitride (MoN), niobium nitride (NbN);a carbide, including but not limited to titanium carbide (TiC) titaniumaluminum carbide (TiAlC), tantalum carbide (TaC), hafnium carbide (HfC),and combinations thereof. In various embodiments, a conductive materialor a combination of multiple conductive materials can serve as both gateconductor and WFM.

In one or more embodiments, a top spacer layer 180 can be formed on theconductive gate fill 170, work function metal (WFM) layer, and gatedielectric layer 160. The top spacer layer 180 can be formed by ablanket or directional deposition with or without an etch-back. The topspacer layer 180 can be an electrically insulating dielectric material,for example, silicon oxide (SiO), silicon nitride (SiN), siliconoxynitride (SiON), a low-k dielectric material, or a combinationthereof.

In one or more embodiments, a top source/drain 190 can be formed on thevertical fin by epitaxial growth. The top source/drain 190 can ben-doped or p-doped to form a vertical transport fin field effecttransistor (VT FinFET) device. In various embodiments, the topsource/drain 190 may cover and extend beyond the edges of the verticalfin, such that the top source/drain 190 does not have the same shape asthe vertical fin. The bottom source/drain 140 can extend beyond theedges of the vertical fin, or can be a rectangular region in thesubstrate below one or more vertical fin(s). An interlayer dielectric(ILD) layer can be formed on the gate structure and source/drains, wherethe ILD layer can be an electrically insulating dielectric material.

In one or more embodiments, a top source/drain contact 200 can be formedto the top source/drain 190, and a bottom source/drain contact 210 canbe formed to the bottom source/drain 140. The top source/drain contact200 and bottom source/drain contact 210 can be a conductive material,for example, a metal, a metal compound, or a combination thereof. Thestructure may further include other contacts, such as a gate contact.The contact material(s) can be tungsten (W), aluminum (Al), copper (Cu),cobalt (Co), nickel (Ni), titanium (Ti), ruthenium (Ru), molybdenum(Mo), or any other suitable conductive material. The metal contact canfurther include a barrier layer. The barrier layer can be titaniumnitride (TiN), tantalum nitride (TaN), hafnium nitride (HfN), niobiumnitride (NbN), tungsten nitride (WN), tungsten carbon nitride (WCN), orcombinations thereof, where the barrier layer can prevent diffusionand/or alloying of the metal contact fill material with the top sourcedrain material, and/or other anode/cathode material.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates other rise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms ended to encompass orientations of the devicein use or operation addition A the orientation depicted in the FIGS. Forexample, if the device in the FIGS. is turned over, elements describedas “below” or “beneath” other elements or features would then beoriented “above” the other elements or features. Thus, the term “below”can encompass both an orientation of above and below. The device can beotherwise oriented (rotated 90 demes or at other orientations), and thespatially relative descriptors used herein can be interpretedaccordingly. In addition, it will also be understood that when a layeris referred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers can also bepresent.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Having described preferred embodiments of a device and method offabricating the device (which are intended to be illustrative and notlimiting), it is noted that modifications and variations can be made bypersons skilled in the art in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A method of forming a vertical fin havingmultiple arms, comprising: heat treating a periodic array of openingshaving an irregular shape in a substrate, wherein walls of substratematerial are disposed between adjacent openings to reduce the surfacearea of the openings; and etching the openings with a crystal-planeselective etch to form squared openings in the substrate.
 2. The methodof claim 1, further comprising, forming a mask over a plurality ofsquared openings and at least a portion of the walls between the squaredopenings that intersect.
 3. The method of claim 2, further comprising,removing the portions of the substrate and walls not covered by the maskto form a two-dimensional vertical fin on the substrate.
 4. The methodof claim 3, wherein the two-dimensional vertical fin has a shapeselected from the group consisting of a cross shape, an H-shape, a fenceshape, and a lattice-shape.
 5. The method of claim 1, wherein theperiodic array of irregular openings is arranged as a square lattice, arectangular lattice, a hexagonal lattice with vertical columns, or ahexagonal lattice with horizontal rows.
 6. The method of claim 5,wherein the periodic array of openings having the irregular shape isarranged as a rectangular lattice having walls with differentthicknesses between horizontally adjacent openings than verticallyadjacent openings.
 7. The method of claim 1, wherein the heat treatingis selected from the group consisting of a furnace anneal, a rapidthermal anneal (RTA), a flash anneal, a laser anneal, or a combinationthereof.
 8. The method of claim 7, wherein the heat treating isconducted at a temperature in a range of about 400° C. to about 1200° C.9. The method of claim 7, wherein the heat treating is conducted for aduration in a range of about 5 seconds (sec) to about 30 minutes (min).10. The method of claim 7, wherein the heat treating is conducted in anatmosphere including a reducing gas selected from the group consistingof hydrogen gas (H₂), deuterium (D₂), and combinations thereof.
 11. Amethod of forming a vertical fin having multiple arms, comprising:forming a periodic array of openings having an irregular shape in asubstrate, wherein walls of substrate material are disposed betweenadjacent openings; heat treating the substrate and openings to reducethe surface area of the openings; and etching the openings with acrystal-plane selective etch to form squared openings in the substrate.12. The method of claim 11, wherein the substrate material is asemiconductor material selected from the group consisting of singlecrystal silicon (c-Si), silicon-germanium (SiGe), and germanium (Ge),and a {110} crystal plane of the substrate material is selectivelyetched.
 13. The method of claim 12, wherein the crystal-plane selectiveetch is a wet etch using ammonium hydroxide (NH₃OH) or a gas etch usinghydrogen chloride (HCl).
 14. The method of claim 11, wherein thesubstrate material is a III-V semiconductor material and a {111} crystalplane of the substrate material is selectively etched.
 15. Atwo-dimensional vertical fin field effect transistor device, comprising:a two-dimensional vertical fin having intersecting arms with squarecorners where perpendicular crystal planes meet.
 16. The two-dimensionalvertical fin field effect transistor device of claim 15, wherein thetwo-dimensional vertical fin is a semiconductor material selected fromthe group consisting of single crystal silicon (c-Si), silicon-germanium(SiGe), and germanium (Ge).
 17. The two-dimensional vertical fin fieldeffect transistor device of claim 15, wherein the perpendicular crystalplanes are {110} and {−110}, and the square corners are atomicallysharp.
 18. The two-dimensional vertical fin field effect transistordevice of claim 15, wherein the each of the intersecting arms has athickness in a range of about 5 nm to about 20 nm.
 19. Thetwo-dimensional vertical fin field effect transistor device of claim 15,further comprising a top source/drain on the two-dimensional verticalfin, wherein the top source/drain has the same two-dimensional shape asthe two-dimensional vertical fin.
 20. The two-dimensional vertical finfield effect transistor device of claim 19, further comprising a bottomsource/drain adjoining a side of the two-dimensional vertical finopposite the top source/drain.